Spotting is very light bleeding, like what you might typically have at the beginning or end of your period. It can vary in color - pink, red, brown. Vaginal bleeding is heavier, like your period.
There are many reasons for spotting or vaginal bleeding throughout your pregnancy. Some are benign, such as implantation bleeding, which occurs 8-10 days after ovulation when the fertilized egg implants in the uterine wall. If you've already gotten a positive pregnancy test and you're bleeding, it's not implantation bleeding.
Bleeding can be a sign of something more serious, such as a miscarriage, ectopic pregnancy, or molar pregnancy, especially if it's accompanied by cramps. Bleeding occurs in 25% and only half of those end in a miscarriage, so the chances are small. If you have an ultrasound between 7 and 11 weeks and the heartbeat was strong, your chances of continuing the pregnancy are very good (90%).
Third trimester bleeding might be caused by problems with your placenta or premature labor. Placenta previa is a complication in which the placenta grows in the lowest part of the womb (uterus) and covers all or part of the cervix. Premature labor is labor that starts at less than 37 weeks.